Thanks for your explaination and links ! it was my entry point for the conversion and the sharing info that make me to buy the duet and do the modification !!
i have still to manage the wiring of the fan (enclosure and cold end cooling fan are connected together)
i have set my motor to 500mA
I didn't connect the BLtouch in the same way than you. I found an alternate that use the probe pin for + and - and use the pin for Heater 7 from the extend connector.
My screen is a 5" so i still have to design an enclosure.
But again : Many many thanks !!